192 SODA OR CAUSTIC SODA. 



per cent, of water,] at from 10s. to 12s. a cwt., has not as yet been ex- 

 tensively tried as a means of promoting vegetation. The lowness of its 

 price, however, and the fact that it is an article of extensive home man- 

 ufacture, conjoined with the encouragement we derive from theoretical 

 considerations — all unite in suggesting the propriety of a series of ex- 

 periments with the view of determining its real value to the practical 

 agriculturist. The mode in which theory indicates that this compound 

 is likely to act in promoting vegetation — as well as the crops to which it 

 may be expected to be especially useful, will come under our considera- 

 tion hereafter. 



Besides the common carbonate of soda above described, and which in 

 the neighbourhood of Newcastle is manufactured from common salt to 

 the amount of 30 or 40 thousand tons every year, there occur in natuie 

 two other compounds of soda with carbonic acid, in which the latter 

 substance is present in larger quantity than in the soda of the shops. 

 The sesqui-carhonate, containing one half more carbonic acid, occurs in 

 the soil in many warm climates (Egypt, India, South America, &c.), 

 and at Fezzan, in Africa, is met with as a mineral deposit of such 

 thickness as in that dry climate to allow of its being employed as a 

 building stone. 



The 6i-carbonate is contained in the waters of many lakes? in Hunga- 

 ry, in Asia, &c., and in many springs in all parts of the world. There 

 can be no doubt that the waters of such springs are fitted to promote the 

 fertility, espeaiftlly of pasture land, to which they may be applied either 

 by artificial irrigation, or by spontaneous overflow from natural outlets. 

 Some of the Harrowgate waters contain a sensible quantity of this bi- 

 carbonate, and over a large portion of the Yorkshire coal-field, a bed of 

 rock is found, at various depths, the springs from which hold in solution 

 a considerable portion of this salt. The Holbeck water of Leeds, ac- 

 cording to Mr. West, owes its softness to the pijesence of this carbonate, 

 and the water from the coal-mines in the neighbourhood of AVakefield 

 is occasionally so charged with it, as to form troublesome saline incrus- 

 tations on the bottoms of the steam boilers. Where these waters- occur 

 in sufficient abundance, they should not be permitted to escape into tlie 

 rivers, until they have previously been employed in irrigating the land. 



It has occasionally been observed that natural springs in some locali- 

 ties impart a degree of luxuriance to natural pasture, which is not to be 

 accounted for by the mere effect of a constant supply of water. In 

 such cases, the springs may be expected to contain some alkaline, or 

 other mineral ingredient, which the soil is unable to supply to the plants 

 which grow upon it, either in sufficient abundance, or with sutficient 

 rapidity. 



5°. Soda or Caustic Soda. — When a solution of the common soda of 

 the shops is boiled with quick-lime, it is deprived of its carbonic acid, 

 and like the carbonate of potash (p. 187) is brought into the caustic state. 

 In this state it destroys animal and vegetable substances, and, unless 

 very dilute, is injurious to animal and vegetable life. 



When common salt (chloride of sodium) is mixed with quick-lime in 

 compost heaps, it is deprived by the lime of a portion of its chlorine, 

 and is partially converted into this caustic soda. The action of the soda 

 in this state is similar to that of caustic potash^ Not only does it readi- 



